The present invention relates to a rod assembly and device for trenchless rehabilitation of pipelines.
The following discussion of related art is provided to assist the reader in understanding the advantages of the invention, and is not to be construed as an admission that this related art is prior art to this invention.
Trenchless rehabilitation of pipelines involves the use of devices in which a new pipe is drawn into an old pipe laid underground previously. The old pipe can either be completely replaced and destroyed in the soil, with the generated fragments displaced radially in the soil, or the old pipe can be pushed out of the soil. The destruction of the old pipe is realized by an upsizing head having an outer diameter which is greater than the inner diameter of the old pipe. The upsizing head is pulled through the old pipe so as to burst the old pipe from within and to displace the fragments into the surrounding soil. The new pipe can be directly attached to the upsizing head so that the destruction of the old pipe is accompanied with an installation of the new pipe. Pushing out the old pipe involves the use of an adapter which is attached to the trailing end of the old pipe. As the old pipe steadily exits the borehole, portions thereof are periodically cut away and disposed of, while a new pipe is pulled in at the same time by attaching it to the adapter.
In the event, there is no intent to fully replace the old pipe but the inside of the old pipe should rather be rehabilitated by applying a lining, a new pipe, configured as a so-called “liner”, is periodically drawn into the old pipe. The liner involves a tube or hose of a wall thickness which is less than the wall thickness of a new pipe.
A pulling device is used to draw in the new pipe for trenchless rehabilitation of pipelines and is normally arranged in a pit adjacent to the portion of the old pipe to be rehabilitated. The pulling device is connected by a traction member with the upsizing head or adapter to which the new pipe is attached. Cable winches have been used as pulling devices because of their reasonable costs, however only fairly small pulling forces can be generated. Therefore, the use of cable winches has been limited to a trenchless replacement of pipelines of small diameter or applying a liner for lining pipelines of average diameter. In many cases, the use of hydraulic linear pulling devices has been proposed which have a drive element that can be connected temporarily with the pulling element and is moved back and forth by one or more hydraulic cylinders cyclically in a direction of the pipe length axis so as to incrementally pull in the new pipe into the soil.
These linear pulling devices are normally combined with a traction member in the form of a rod assembly which has a plurality of interconnected rod sections. Rod assemblies are easy to handle because of the subdivision into individual rod sections that allows the length of the rod assembly to be extended or shortened to suit the work progress at hand by adding or detaching individual rod sections.
The individual rod sections of a rod assembly are normally connected to one another via thread connections which are widely available as they can be produced easily and inexpensively. However, connecting the rod sections to one another becomes very cumbersome and time-consuming. This is especially true when using mechanical disassembly and connection devices since the rod sections have a size and weight which no longer can be handled manually when using powerful linear pulling devices. In addition, care is required to maintain the threaded components of the threaded connection clean enough because dirty threaded connections wear off quickly and there is a risk that the dirty threaded connection becomes jammed and may no longer be detachable. Maintaining the threaded components clean is however labor-intensive and time-consuming at construction sites.
To address these problems, U.S. Pat. No. 5,980,157 proposes a connection of individual rod sections via a plug connection, whereby one end of each rod section is provided with a hook-shaped connection part which cooperates with a ladder-like projection on the other end of each rod section to thereby enable a transmission of pulling forces. The contact surfaces of the connection parts of both rod sections to transmit the pulling and compressive forces are hereby configured planar. While this configuration results in a uniform distribution of the force across the entire contact surface when transmitting pure pulling or compressive forces, a simultaneous presence of a bending moment causes an adverse stress distribution in the area of the contact surface so that the service life of the connection parts and thus the rod sections is reduced.
It would therefore be desirable and advantageous to address this problem and to obviate other prior art shortcomings.